Browsers use the DOCTYPE declaration to choose whether to show the document using a mode that is more compatible with Web standards or with old browser bugs. Using a correct and modern DOCTYPE declaration at the start of your HTML will improve browser standards compliance.
The RTCDataChannel interface is a feature of the WebRTC API which lets you open a channel between two peers over which you may send and receive arbitrary data. The API is intentionally similar to the WebSocket API, so that the same programming model can be used for each.
With CSS3, you can apply multiple backgrounds to elements. These are layered atop one another with the first background you provide on top and the last background listed in the back. Only the last background can include a background color.
Specificity is the means by which browsers decide which CSS property values are the most relevant to an element and, therefore, will be applied. Specificity is based on the matching rules which are composed of CSS selectors of different sorts.
The background-size CSS property makes it possible to adjust the size of background images, instead of the default behavior of tiling the image at its full size. You can scale the image upward or downward as desired.
The CSS3 Flexible Box, or flexbox, is a layout mode providing for the arrangement of elements on a page such that the elements behave predictably when the page layout must accommodate different screen sizes and different display devices. For many applications, the flexible box model provides an improvement over the block model in that it does not use floats, nor do the flex container's margins collapse with the margins of its contents.
CSS gradients are new types of <image> added in the CSS3 Image Module. Using CSS gradients lets you display smooth transitions between two or more specified colors. This lets you avoid using images for these effects, thereby reducing download time and bandwidth usage. In addition, because the gradient is generated by the browser, objects with gradients look better when zoomed, and you can adjust your layout much more flexibly.
Stacking context is the three-dimensional conceptualization of HTML elements along an imaginary z-axis relative to the user who is assumed to be facing the viewport or the webpage. HTML elements occupy this space in priority order based on element attributes.
Microdata is a WHATWG HTML specification used to nest metadata within existing content on web pages. Search engines, web crawlers, and browsers can extract and process microdata from a web page and use it to provide a richer browsing experience for users. Search engines benefit greatly from direct access to this structured data because it allows search engines to understand the information on web pages and provide more relevant results to users. Microdata uses a supporting vocabulary to describe an item and name-value pairs to assign values to its properties. Microdata is an attempt to provide a simpler way of annotating HTML elements with machine-readable tags than the similar approaches of using RDFa and microformats.
The HTML5 specification brings several new elements to web developers allowing them to describe the structure of a web document with standard semantics. This document describes these elements and how to use them to define the desired outline for any document.